Methods and systems for determining resistance of power conductors

ABSTRACT

Methods of powering a radio that is mounted on a tower of a cellular base station are provided in which a direct current (“DC”) power signal is provided to the radio over a power cable and a voltage level of the output of the power supply is adjusted so as to provide a substantially constant voltage at a first end of the power cable that is remote from the power supply. Related cellular base stations and programmable power supplies are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 120 as acontinuation of U.S. patent application Ser. No. 16/403,773, filed May6, 2019, which is a continuation of U.S. patent application Ser. No.14/701,904, filed May 1, 2015 and issued as U.S. Pat. No. 10,281,939,which is a continuation-in-part of U.S. patent application Ser. No.14/321,897, filed Jul. 2, 2014 and issued as U.S. Pat. No. 9,448,576,which in turn claims priority to U.S. Provisional Patent ApplicationSer. No. 61/940,631, filed Feb. 17, 2014, the entire contents of each ofwhich is incorporated herein by reference as if set forth in itsentirety.

FIELD OF THE INVENTION

The present invention relates generally to cellular communicationssystems and, more particularly, to cellular communications power supplysystems.

BACKGROUND

Cellular base stations typically include, among other things, a radio, abaseband unit, and one or more antennas. The radio receives digitalinformation and control signals from the baseband unit and modulatesthis information into a radio frequency (“RF”) signal that istransmitted through the antennas. The radio also receives RF signalsfrom the antenna and demodulates these signals and supplies them to thebaseband unit. The baseband unit processes demodulated signals receivedfrom the radio into a format suitable for transmission over a backhaulcommunications system. The baseband unit also processes signals receivedfrom the backhaul communications system and supplies the processedsignals to the radio. A power supply may also be provided that generatessuitable direct current (“DC”) power signals for powering the basebandunit and the radio. For example, the radio is often powered by a(nominal) 48 Volt DC power supply in cellular systems that are currentlyin use today. A battery backup is also typically provided to maintainservice for a limited period of time during power outages.

In order to increase coverage and signal quality, the antennas in manycellular base stations are located at the top of an antenna tower, whichmay be, for example, about fifty to two hundred feet tall. Antennas arealso routinely mounted on other elevated structures such as, forexample, buildings, utility poles and the like. Until fairly recently,the power supply, baseband unit and radio were all located in anequipment enclosure at the bottom of the antenna tower or other elevatedstructure to provide easy access for maintenance, repair and/or laterupgrades to the equipment. Coaxial cable(s) were routed from theequipment enclosure to the top of the antenna tower and were used tocarry RF signals between the radios and the antennas.

FIG. 1 is a schematic diagram that illustrates a conventional cellularbase station 10. As shown in FIG. 1 , the depicted cellular base station10 includes an equipment enclosure 20 and an antenna tower 30. Theequipment enclosure 20 is typically located at the base of the antennatower 30, as shown in FIG. 1 . A baseband unit 22, a radio 24 and apower supply 26 are located within the equipment enclosure 20. Thebaseband unit 22 may be in communication with a backhaul communicationssystem 44. A plurality of antennas 32 (e.g., three sectorized antennas32-1, 32-2, 32-3) are located at the top of the antenna tower 30. Threecoaxial cables 34 (which are bundled together in FIG. 1 to appear as asingle cable) connect the radio 24 to the antennas 32. The antennas 32are passive (unpowered) devices and hence none of the equipment at thetop of the tower 30 requires electrical power. While the cellular basestation 10 of FIG. 1 (and various other cellular base stations shown insubsequent figures) is shown as a having a single baseband unit 22 andradio 24 to simplify the drawings and description, it will beappreciated that cellular base stations routinely have multiple basebandunits 22 and radios 24 (and additional antennas 32), with three, six,nine or even twelve baseband units 22 and radios 24 being common instate-of-the-art systems.

In recent years, a shift has occurred and the radio 24 is now moretypically located at the top of the tower 30 in new or upgraded cellularinstallations. Radios that are located at the top of the tower 30 aretypically referred to as remote radio heads (“RRH”) 24′. Using remoteradio heads 24′ may significantly improve the quality of the cellulardata signals that are transmitted and received by the cellular basestation, as the use of remote radio heads 24′ may reduce signaltransmission losses and noise. In particular, as the coaxial cables 34that connect radios 24 that are located at the base of an antenna tower30 to antennas 32 that are mounted near the top of the antenna tower 30may have lengths of 100-200 feet or more, the signal loss that occurs intransmitting signals at cellular frequencies (e.g., 1.8 GHz, 3.0 GHz,etc.) over these coaxial cables 34 may be significant, as at thesefrequencies the coaxial cables 34 tend to radiate RF signal energy.Because of this loss in signal power, the signal-to-noise ratio of theRF signals may be degraded in systems that locate the radio 24 at thebottom of the antenna tower 30 as compared to cellular base stationshaving remote radio heads 24′ that are located at the top of the tower30 next to the antennas 32 (note that signal losses in the cablingconnection between the baseband unit 22 at the bottom of the tower 30and the remote radio head 24′ at the top of the tower 30 may be muchsmaller, as these signals are transmitted at baseband or intermediatefrequencies as opposed to RF frequencies, and because these signals maybe transmitted up the antenna tower 30 over fiber optic cables, whichmay exhibit lower losses).

FIG. 2 is a schematic diagram that illustrates a cellular base station10′ according to this newer architecture. As shown in FIG. 2 , thebaseband unit 22 and the power supply 26 may still be located at thebottom of the tower 30 in the equipment enclosure 20. The radio 24 inthe form of an remote radio head 24′ is located at the top of the tower30 immediately adjacent to the antennas 32. While the use oftower-mounted remote radio heads 24′ may improve signal quality, italso, unfortunately, requires that DC power be delivered to the top ofthe tower 30 to power the remote radio head 24′. As shown in FIG. 2 ,typically a fiber optic cable 38 connects the baseband unit 22 to theremote radio head 24′ (as fiber optic links may provide greaterbandwidth and lower loss transmissions), and a separate or combined(“composite”) power cable 36 is provided for delivering the DC powersignal to the remote radio head 24′. The separate power cable 36 istypically bundled with the fiber optic cable 38 so that they may berouted up the tower 30 together. In other cases (not shown), a hybridfiber optic/power trunk cable 40 may be run up the tower 30. Such trunkcables 40 typically have junction enclosures on either end thereof, anda first set of data and power jumper cables are used to connect thejunction enclosure on the ground end of the trunk cable 40 to thebaseband unit(s) 22 and power supply 26, and a second set of data andpower (or combined data/power) jumper cables are used to connect thejunction enclosure at the top of the tower 30 to the remote radio heads24.

Another change that has occurred in the cellular industry is a rapidincrease in the number of subscribers as well as a dramatic increase inthe amount of voice and data traffic transmitted and received by atypical subscriber. In response to this change, the number of remoteradio heads 24′ and antennas 32 that are being mounted on a typicalantenna tower 30 has also increased, with twelve remote radio heads 24′and twelve or more antennas 32 being a common configuration today.Additionally, higher power remote radio heads 24′ are also being used.These changes may result in increased weight and wind loading on theantenna towers 30 and the need for larger, more expensive trunk cables40.

SUMMARY

Pursuant to embodiments of the present invention, methods of powering aradio that is mounted on a tower of a cellular base station (or otherlocation remote from an associated baseband unit) are provided in whicha DC power signal is output from a power supply and the DC power signalthat is output from the power supply is supplied to the radio over apower cable. A voltage level of the DC power signal that is output fromthe power supply is adjusted so that the DC power signal at a radio endof the power cable that is remote from the power supply has asubstantially constant voltage notwithstanding variation in a currentlevel of the DC power signal.

In some embodiments, the power supply may be a programmable powersupply, and the method may further include inputting information to thepower supply from which the voltage level of the DC power signal that isoutput from the power supply can be computed that will provide the DCpower signal at the radio end of the power cable that has thesubstantially constant voltage. In such embodiments, the informationthat is input to the power supply may be a resistance of the powercable, or may be a length of the power cable and a diameter of theconductive core of the power cable.

In some embodiments, a current level of the DC power signal that isoutput from the power supply may be measured, and the voltage level ofthe DC power signal that is output by the power supply may beautomatically adjusted in response to changes in the measured outputcurrent of the DC power signal that is output from the power supply toprovide the DC power signal at the radio end of the power cable that hasthe substantially constant voltage.

In some embodiments, the programmable power supply may be a DC-to-DCconverter that receives a DC power signal that is output from a secondpower supply and adjusts a voltage level of the DC power signal that isoutput from the second power supply to provide the DC power signal atthe radio end of the power cable that has the substantially constantvoltage. The substantially constant voltage may be a voltage thatexceeds a nominal power signal voltage of the radio and which is lessthan a maximum power signal voltage of the radio.

In some embodiments, a signal may be transmitted over the power cablethat is used to determine an electrical resistance of the power cable.In some embodiments, the substantially constant voltage may besignificantly higher than a maximum power signal voltage of the radio,and a tower-mounted DC-to-DC converter may be used to reduce a voltageof the power signal at the radio end of the power cable to a voltagethat is less than the maximum power supply voltage of the radio.

Pursuant to further embodiments of the present invention, cellular basestation systems are provided that include a tower with at least oneantenna mounted thereon, an RRH mounted on the tower, a baseband unitthat is in communication with the remote radio head, a programmablepower supply located remotely from the remote radio head; and a powercable having a first end that receives a DC power signal from theprogrammable power supply and a second end that provides the DC powersignal to the remote radio head. The programmable power supply isconfigured to provide a substantially constant voltage at the second endof the power cable by adjusting a voltage level of the DC power signaloutput by the programmable power supply based on the current leveloutput by the programmable power supply and a resistance of the powercable.

In some embodiments, the programmable power supply may include a userinterface that is configured to receive a resistance of the power cableand/or information regarding characteristics of the power cable fromwhich the resistance of the power cable may be calculated. Theprogrammable power supply may further include a current measurementmodule that measures a current output by the power supply. Theprogrammable power supply may also include a feedback loop that adjuststhe voltage level of the DC power signal output of the power supplybased on the measured current output by the power supply.

Pursuant to still further embodiments of the present invention,programmable power supplies are provided that include an input; aconversion circuit that is configured to convert an input signal into aDC output signal that is output through an output port; a current sensorthat senses an amount of current output through the output port; a userinput that is configured to receive information relating to theresistance of a cabling connection between the programmable power supplyoutput port and a radio; and a control module that is configured tocontrol the conversion circuit in response to information relating tothe resistance of the cabling connection and the sensed amount ofcurrent to adjust the voltage of the output signal that is outputthrough the output port so that the voltage at the far end of thecabling connection may remain substantially constant despite changes inthe current drawn by the radio.

In some embodiments, the information relating to the resistance of thecabling connection may comprise a length of the cabling connection and asize of the conductor of the cabling connection.

Pursuant to additional embodiments of the present invention, methods ofpowering a cellular radio that is located remotely from a power supplyand an associated baseband unit and that is connected to the powersupply by a cabling connection are provided in which a DC power signalis output from the power supply and the DC power signal that is outputfrom the power supply is supplied to the radio over the cablingconnection. A voltage level of the DC power signal that is output fromthe power supply is adjusted in response to a current level of the DCpower signal that is output from the power supply so that the voltage ofthe DC power signal at a radio end of the cabling connection ismaintained at a pre-selected level, range or pattern.

In some embodiments, the voltage level of the DC power signal that isoutput from the power supply is adjusted in response to a feedbacksignal that is transmitted to the power supply from a remote location.The feedback signal may include information regarding the measuredvoltage of the DC power signal at the radio end of the power cable.

Pursuant to yet additional embodiments of the present invention, methodsof powering a radio that is mounted on a tower of a cellular basestation (or other location remote from an associated baseband unit) areprovided in which a DC power signal is output from a power supply andthe DC power signal that is output from the power supply is supplied tothe radio over a power cable. A voltage of the DC power signal ismeasured at a radio end of the power cable that is remote from the powersupply. Information regarding the measured voltage of the DC powersignal at the radio end of the power cable is communicated to the powersupply. A voltage level of the DC power signal that is output from thepower supply is adjusted in response to the received informationregarding the measured voltage of the DC power signal at the radio endof the power cable.

In some embodiments, the voltage level of the DC power signal that isoutput from the power supply may be adjusted in response to the receivedinformation to maintain the DC power signal at the radio end of thepower cable at a substantially constant voltage notwithstandingvariation in a current level of the DC power signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified, schematic view of a traditional cellular basestation architecture.

FIG. 2 is a simplified, schematic view of a conventional cellular basestation in which a remote radio head is located at the top of theantenna tower.

FIG. 3 is a simplified, schematic view of a cellular base stationaccording to embodiments of the present invention.

FIG. 4 is a schematic block diagram of a programmable power supplyaccording to embodiments of the present invention.

FIG. 5 is a schematic block diagram of a programmable power supplyaccording to further embodiments of the present invention.

FIG. 6 is a simplified, schematic view of a cellular base stationaccording to still further embodiments of the present invention.

FIG. 7 is a simplified, schematic view of a cellular base stationaccording to yet additional embodiments of the present invention.

FIG. 8 is a simplified, schematic view of a cellular base stationaccording to yet further embodiments of the present invention.

FIG. 9 is a flow chart illustrating operations of methods according toembodiments of the present invention.

FIG. 10 is a perspective view of an end portion of a hybrid power/fiberoptic cable that may be used in cellular base stations according toembodiments of the present invention.

FIG. 11 is a schematic drawing illustrating how a jumper cable thatincludes a shunt capacitance unit may be used to connect a junctionenclosure to a remote radio head in cellular base stations according toembodiments of the present invention.

FIG. 12 is a partially-exploded perspective view of a shunt capacitanceunit according to certain embodiments of the present invention.

FIG. 13 is a circuit diagram of a shunt capacitance unit that includesan avalanche diode according to embodiments of the present invention.

FIG. 14 is a circuit diagram of a shunt capacitance unit that includesan avalanche diode according to further embodiments of the presentinvention.

FIG. 15 is a schematic diagram of a cellular base station according tostill further embodiments of the present invention.

DETAILED DESCRIPTION

Pursuant to embodiments of the present invention, methods for deliveringDC power to a remote radio head (“RRH”) of a cellular base station areprovided, along with related cellular base stations, programmable powersupplies, power cables and other equipment. These methods, systems,power supplies, cables and equipment may allow for lower power supplycurrents, which may reduce the power loss associated with delivering theDC power signal from the power supply at the base of a tower of thecellular base station to the remote radio head at the top of the tower.Since cellular towers may be hundreds of feet tall and the voltage andcurrents required to power each remote radio head may be quite high(e.g., about 50 Volts at about 20 Amperes of current), the power lossthat may occur along the hundreds of feet of cabling may be significant.Thus, the methods according to embodiments of the present invention mayprovide significant power savings which may reduce the costs ofoperating a cellular base station. Additionally, since the cellular basestations may use less power, the cellular base stations according toembodiments of the present invention may require fewer back-up batterieswhile maintaining operation for the same period of time during a poweroutage. This reduction in the amount of back-up batteries may representa significant additional cost savings.

The DC voltage of a power signal that is supplied to a remote radio headfrom a power supply over a power cable may be determined as follows:V _(RRH) =V _(PS) −V _(Drop)  (1)where V_(RRH) is the DC voltage of the power signal delivered to theremote radio head, V_(PS) is the DC voltage of the power signal that isoutput by the power supply, and V_(Drop) is the decrease in the DCvoltage that occurs as the DC power signal traverses the power cableconnecting the power supply to the remote radio head. It will beappreciated that the power cable that connects the power supply to theremote radio head will typically have multiple segments. For example, incellular base stations in which a trunk cable is used, the power cablingconnection will typically include a power jumper cable that connects thepower supply to one end of the trunk cable, the power conductors in thetrunk cable, and a power jumper cable that connects the other end of thetrunk cable to the remote radio head. V_(Drop) in Equation (1) may bedetermined according to Ohm's Law as follows:V _(Drop) =I _(Cable) *R _(Cable)  (2)where R_(Cable) is the cumulative electrical resistance (in Ohms) of thepower cable connecting the power supply to the remote radio head andI_(Cable) is the average current (in Amperes) flowing through the powercable to the remote radio head and back to the power supply.

The cumulative electrical resistance R_(Cable) of the power cable isinversely proportional to the diameter of the conductor of the powercable (assuming the conductors have a circular cross-section). Thus, thelarger the diameter of each conductor (i.e., the lower the gauge of theconductor), the lower the resistance of the power cable. Typically,power cables utilize copper conductors due to the low resistance ofcopper. Copper resistance is specified in terms of unit length,typically milliohms (mΩ)/ft; as such, the cumulative electricalresistance R_(Cable) of the power cable increases with the length of thepower cable. Thus, the longer the power cable, the higher the voltagedrop V_(Drop).

Typically, a minimum required voltage for the power signal, a nominal orrecommended voltage for the power signal and a maximum voltage for thepower signal will be specified for the remote radio head. Thus, thepower supply at the base of the tower must output a voltage V_(PS) suchthat V_(RRH) will be between the minimum and maximum specified voltagesfor the power signal of the remote radio head. As V_(Drop) is a functionof the current I_(Cable) that is supplied to the remote radio head (seeEquation (2) above), if V_(PS) (the voltage output by the power supply)is constant, then the voltage V_(RRH) of the power signal that isdelivered to the remote radio head will change with the variation incurrent I_(Cable) drawn by the remote radio head from the power supply.Conventionally, the voltage output of the power signal by the powersupply (V_(PS)) is set to ensure that a power signal having the nominalspecified voltage is supplied to the remote radio head (or at least avalue above the minimum required voltage for the power signal) when theremote radio head draws the maximum anticipated amount of current fromthe power supply.

The power that is lost (P_(Loss)) in delivering the power signal to theremote radio head over a power cable may be calculated as follows:P _(Loss) =V _(Drop) *I _(Cable)=(I _(Cable) *R _(Cable))*I _(Cable) =I_(Cable) ² *R _(Cable)  (3)In order to reduce or minimize P_(Loss), the power supply may be set tooutput a DC power signal that, when it arrives at the remote radio head,will have a voltage that is near the maximum voltage specified for theremote radio head, as the higher the voltage of the power signal that isdelivered to the remote radio head, the lower the current I_(Cable) ofthe power signal on the power cable. As is apparent from Equation (3)above, the lower the current I_(Cable) of the power signal on the powercable, the lower the power loss P_(Loss).

Pursuant to embodiments of the present invention, the power supply maycomprise a programmable power supply which may (1) sense the currentbeing drawn by the remote radio head (or another equivalent parameter)and (2) adjust the voltage of the power signal that is output by thepower supply to substantially maintain the voltage of the power signalthat is supplied to the remote radio head at or near a desired value,which may be, for example, the maximum voltage for the power signal thatmay be input to the remote radio head. In order to accomplish this, theresistance of the power cable may be input to the programmable powersupply or, alternatively, other information such as, for example, thelength and size of the power cable, or the impedance of the power cable,may be input to the programmable power supply and the programmable powersupply may determine the resistance of the power cable from thisinformation. As the current drawn by the remote radio head varies, theprogrammable power supply may adjust the voltage of its output powersignal to a voltage level that will deliver a power signal having apreselected voltage (e.g., the maximum supply voltage of the remoteradio head minus a buffer) to the remote radio head. As shown byEquation (3) above, this will reduce the power loss along the powercable, and hence may reduce the cost of powering the remote radio head.As a typical remote radio head may require about a kilowatt of power andmay run 24 hours a day, seven days a week, and as a large number ofremote radio heads may be provided at each cellular base station (e.g.,three to twelve), the power savings may be significant.

Embodiments of the present invention will now be discussed in moredetail with reference to FIGS. 3-14 , in which example embodiments ofthe present invention are shown.

FIG. 3 is a schematic block diagram of a cellular base station 100according to embodiments of the present invention. As shown in FIG. 3 ,the cellular base station 100 includes an equipment enclosure 20 and atower 30. The tower 30 may be a conventional antenna or cellular toweror may be another structure such as a utility pole or the like. Abaseband unit 22, a first power supply 26 and a second power supply 28are located within the equipment enclosure 20. An remote radio head 24′and plurality of antennas 32 (e.g., three sectorized antennas 32-1,32-2, 32-3) are mounted on the tower 30, typically near the top thereof.

The remote radio head 24′ receives digital information and controlsignals from the baseband unit 22 over a fiber optic cable 38 that isrouted from the enclosure 20 to the top of the tower 30. The remoteradio head 24′ modulates this information into an RF signal at theappropriate cellular frequency that is then transmitted through one ormore of the antennas 32. The remote radio head 24′ also receives RFsignals from one or more of the antennas 32, demodulates these signals,and supplies the demodulated signals to the baseband unit 22 over thefiber optic cable 38. The baseband unit 22 processes the demodulatedsignals received from the remote radio head 24′ and forwards theprocessed signals to the backhaul communications system 44. The basebandunit 22 also processes signals received from the backhaul communicationssystem 44 and supplies them to the remote radio head 24′. Typically, thebaseband unit 22 and the remote radio heads 24′ each includeoptical-to-electrical and electrical-to-optical converters that couplethe digital information and control signals to and from the fiber opticcable 38.

The first power supply 26 generates one or more DC power signals. Thesecond power supply 28 in the embodiment of FIG. 3 comprises a DC-to-DCconverter that accepts the DC power signal output by the first powersupply 26 as an input and outputs a DC power signal having a differentvoltage. A power cable 36 is connected to the output of the second powersupply 28 and is bundled together with the fiber optic cable 38 so thatthe two cables 36, 38 may be routed up the tower 30 as an integral unit.In other embodiments, a hybrid power/fiber optic trunk cable 40 may berouted up the tower 30, and jumper cables may be connected between eachend of the trunk cable 40 and the baseband units 22, power supply 28 andremote radio heads 24′. In such embodiments, the power jumper cables andthe power portion of the trunk cable 40 comprise the power cable 36.While the first power supply 26 and the second power supply 28 areillustrated as separate power supply units in the embodiment of FIG. 3 ,it will be appreciated that the two power supplies 26, 28 may becombined into a single power supply unit in other embodiments.

As noted above, pursuant to embodiments of the present invention, DCpower supplies are provided that may deliver a power signal to a remoteradio head 24′ with reduced power loss. In the embodiment of FIG. 3 ,the power supply 28 comprises a programmable power supply that receivesan input DC power signal from power supply 26 and outputs a DC powersignal to the power cable 36. Pursuant to embodiments of the presentinvention, the voltage of the DC power signal output by the power supply28 may vary in response to variations in the current of the DC powersignal drawn from the power supply 28 by the remote radio head 24′. Inparticular, the voltage of the DC power signal output by the powersupply 28 may be set, for example, so that the voltage of the DC powersignal at the far end of the power cable 36 (i.e., the end adjacent theremote radio head 24′) is relatively constant. If the voltage of the DCpower signal at the far end of power cable 36 is set to be at or nearthe maximum specified voltage for the power signal of the remote radiohead 24′, then the power loss associated with supplying the DC powersignal to the remote radio head 24′ over the power cable 36 may bereduced, since the higher DC power signal voltage will correspondinglyreduce the current of the DC power signal that is supplied over thepower cable 36.

State-of-the-art remote radio heads 24′ are often designed to be poweredby a 48 Volt (nominal) DC power signal. While the minimum DC powersignal voltage at which the remote radio head 24′ will operate and themaximum DC power signal voltage that may be provided safely to theremote radio head 24′ without the threat of damage to the remote radiohead 24′ vary, typical values are a 38 Volt minimum DC power signalvoltage and a 56 Volt maximum DC power signal voltage. Thus, accordingto embodiments of the present invention, the programmable power supply28 may be designed to deliver a DC power signal having a relativelyconstant voltage of, for example, about 54 or 52 Volts at the far end ofthe power cable 36 (i.e., about, 2-4 Volts less than the maximum DCpower signal voltage for the remote radio head 24′) in order to reducethe power loss associated with the voltage drop that the DC power signalexperiences traversing the power cable 36.

In order to maintain the voltage of the DC power signal at the far endof the power cable 36 at or near a predetermined value (or within apre-selected range), it may be necessary to know two things. First, thecurrent I_(cable) of the DC power signal drawn from the power supplymust be known, as Equations (1) and (2) show that V_(RRH) is a functionof the current I_(Cable). Second, the resistance R_(Cable) of the powercable 36 must also be known, as it too affects the voltage drop. Theprogrammable power supplies according to embodiments of the presentinvention may be configured to measure, estimate, calculate or receiveboth values.

For example, FIG. 4 is a block diagram of a programmable power supply150 in the form of a DC-to-DC converter according to certain embodimentsof the present invention that may be used as the power supply 28 of FIG.3 . As shown in FIG. 4 , the programmable power supply 150 includes aninput 152, a conversion circuit 154 and an output 156. The power supply150 further includes a current sensor 158, a user input 160, controllogic 162 and a memory 164.

The input 152 may receive a DC power signal such as the DC power signaloutput by power supply 26 of FIG. 3 . The DC power signal that isreceived at input 152 may be a DC power signal having a relativelyconstant voltage in some embodiments. The conversion circuit 154 may bea circuit that is configured to convert the voltage of the signalreceived at input 152 to a different DC voltage. A wide variety of DCconversion circuits are known in the art, including, for example,electronic, electrochemical and electromechanical conversion circuits.Most typically electronic circuits using inductors or transformers areused to provide high efficiency voltage conversion. The output 156 mayoutput the DC power signal having the converted voltage.

The current sensor 158 may be any appropriate circuit that senses thecurrent level of the DC power signal output through the output 156. Forexample, the current sensor 158 may be implemented using a resistorhaving a known value along the power supply conductor or the returnconductor internal to the power supply 158, along with a voltage meterthat measures the voltage drop across the resistor, and the current maythen be calculated according to Ohm's Law. It will also be appreciatedthat the current sensor 158 may be located external to the power supply150 in other embodiments. The current drawn by the remote radio head 24′may vary over time depending upon, for example, the number of carriersthat are transmitting at any given time and whether the remote radiohead 24′ is in a steady-state mode, powering up or rebooting. Thecurrent sensor 158 may sense the current level of the DC power signal atthe output 156 and provide the sensed current level to the control logic162. The control logic 162 may then adjust parameters of the conversioncircuit 154 so as to adjust the voltage of the DC power signal outputthrough output 156 so that the voltage at the far end of the power cable36 that is attached to output 156 may remain, for example, substantiallyconstant despite changes in the current drawn by the remote radio head24′ and corresponding changes in the voltage drop that occurs over thepower cable 36.

While FIG. 4 illustrates a power supply 150 that comprises a DC-to-DCconverter, it will be appreciated that in other embodiments an AC-to-DCconverter may be used instead. In such embodiments, the input 152receives an alternating current (“AC”) power signal and the conversioncircuit 154 converts the AC power signal to a DC power signal and alsoadjusts the voltage level of the DC power signal that is output throughoutput 156 to an appropriate level in the manner discussed above.

As noted above, in some embodiments, the voltage of the power signalthat is output by the power supply 150 may be set so that the voltage atthe far end of the power cable 36 remains at or near a predeterminedvoltage level that is just under a maximum power signal voltage levelthat is specified for the remote radio head 24′. In order to achievethis, it is necessary to know the voltage drop that the DC power signalwill experience traversing the power cable 36, as this voltage dropaffects the voltage of the DC power signal at the far end of the powercable 36. In some embodiments, the user input 160 to the power supply150 allows a user to input a cumulative resistance value for the powercable 36 which the user may obtain by, for example, calculation (basedon the length, size and material of the conductor of the power cable36), measurement (done, for example, by transmitting a signal over thepower cable 36 and measuring the voltage of the signal output at the farend of the power cable 36) or a combination thereof (e.g., measuring orestimating a cumulative impedance value for the power cable 36 andconverting this cumulative impedance value into a cumulative resistancevalue). In other embodiments, the user may input physicalcharacteristics of the power cable 36 such as size, length, conductormaterial, model number, etc.) and algorithms, equations, look-up tablesand the like that are stored in the memory 164 of the power supply 150may be used to calculate or estimate the resistance of the power cable36. In still other embodiments, the resistance of the power cable 36 mayalready be known because it was measured or otherwise determined by thecable manufacturer. By way of example, the power cable 36 may have theresistance printed on the jacket thereof, coded into a bar code that isprovided on the power cable 36 or stored in an RFID chip that is part ofthe power cable.

In some embodiments, the second power supply 28 of FIG. 3 may further beconfigured to measure a resistance of the power cable 36. For example,FIG. 5 is a block diagram of a programmable power supply 150′ accordingto further embodiments of the present invention that may be used toimplement the power supply 28 of FIG. 3 . The power supply 150′ is verysimilar to the power supply 150 of FIG. 4 , except that it furtherincludes a cable resistance measurement circuit 170 that may be used tomeasure a resistance of the power supply cable. The cable resistancemeasurement circuit 170 may be implemented in a variety of ways. Forexample, in some embodiments, the cable resistance measurement circuit170 may transmit a voltage pulse onto the power cable 36 and measure thereflected return pulse (the far end of the power cable may be terminatedwith a termination having known characteristics). The current of thevoltage pulse may be measured, as well as the voltage level of thereflected return pulse. The control logic 162 may then apply Ohm's lawto calculate the resistance of the power cable 36. In other embodiments,at the far end of the power cable 36 the two conductors thereof may beshorted and a voltage pulse may again be transmitted through the powercable 36. The current level of the pulse and the voltage level of thereturn pulse may be measured and the control logic 162 may again usethese measured values to calculate the resistance of the power cable 36.In other embodiments, the DC resistance can be measured by transmittingalternating current signals at different frequencies over the powercable 36 and measuring the amplitude and phase shift of these signals atthe far end of the power cable 36. The DC resistance may then becalculated using the measured results. Other ways of measuring theresistance of a wire segment are known to those of skill in the art andmay be used instead of the example methods listed above. Additionaltechniques for determining the resistance are also discussed below.

It will also be appreciated that in other embodiments the resistancemeasurement circuit 170 may measure an impedance of the power cable 36and use this measured impedance value to determine the resistance of thepower cable 36. It will also be appreciated that the power supply 150′may alternatively comprise an AC-to-DC converter, similar to powersupply 150 discussed above.

Another technique for reducing the power loss associated with supplyingpower to a tower-mounted remote radio head of a cellular base station isto dramatically increase the voltage of the DC power signal fed to thepower cable that supplies the DC power signal to the remote radio head(i.e., well beyond the maximum specified voltage for the DC power signalthat can be handled by the remote radio head), and then using atower-mounted DC-to-DC converter power supply to step-down the voltageof the DC power signal to a voltage level that is appropriate for theremote radio head. As the increased voltage reduces the currentnecessary to supply the wattage required by the remote radio head, thepower loss along the power cable may be reduced (see Equation (2)above). This is referred to as a “Buck-Boost” scheme where the DC-to-DCconverter at the bottom of the tower is a “Boost” converter thatincreases the voltage of the DC power signal above the necessary levelto operate the remote radio head and the DC-to-DC converter at the topof the tower is a “Buck” converter that reduces the voltage of the DCpower signal to a desired level. FIG. 6 is a simplified, schematic viewof a cellular base station 200 that implements such a technique.

As shown in FIG. 6 , the cellular base station 200 is similar to thecellular base station 100 described above with reference to FIG. 3 ,except that the cellular base station 200 further includes a third powersupply 42 in the form of a tower-mounted DC-to-DC converter. In thedepicted embodiment, the second power supply 28 of FIG. 3 is omitted,and the first power supply 26 is configured to supply a DC power signalhaving a voltage that is significantly higher than the maximum voltagefor the DC power signal that may be supplied to the remote radio head24′ (e.g., a 150 volt DC power signal). This high voltage DC powersignal may experience significantly less power loss when traversing thepower cable 36. The DC-to-DC converter 42 is mounted at the top of thetower 30 between the far end of cable 36 and the remote radio head 24′.The DC-to-DC converter 42 may be a Buck converter that decreases thevoltage of the DC power signal received over the power cable 36 to avoltage level appropriate for supply to the remote radio head 24′.

As is shown in FIG. 7 , in other embodiments, the second power supply 28may be included in the form of, for example, a DC-to-DC Boost powerconverter 28 that supplies a high voltage DC power signal (e.g., 150volts) to the power cable 36. In this embodiment, a DC-to-DC converteris provided at both ends of the power cable 36 so that both of theabove-described techniques for reducing power losses in the power cable36 may be implemented. In particular, the second power supply 28 mayoutput a DC power signal having high voltage (e.g., on the order of 150volts) that fluctuates with power requirements of the remote radio head24′ so that the DC power signal that is supplied at the far end of powercable 36 is set at a relatively constant value. The tower-mountedDC-to-DC converter 42 may be a simple device that down-converts thevoltage of the DC power signal by a fixed amount X. The power supply 28may be programmed to deliver a DC power signal to the tower-mountedDC-to-DC converter 42 that has a voltage level that is set as follows:Voltage of Delivered Power Signal=V _(RRH-Max) −V _(margin) +X  (4)where V_(RRH-Max) is the maximum power signal voltage that the remoteradio head 24′ is specified to handle, V_(margin) is a predeterminedmargin (e.g., 2 Volts), and X is the magnitude of the voltage conversionapplied by the tower-mounted DC-to-DC converter 42.

One disadvantage of the approaches of FIGS. 6 and 7 is that they requirethe installation of additional equipment (i.e., the DC-to-DC converter42) at the top of the tower 30. As the cost associated with sending atechnician up a tower may be very high, there is generally a preferenceto reduce or minimize, where possible, the amount of equipment that isinstalled at the top of a cellular base station tower, and the equipmentthat is installed at the top of cellular towers tends to be expensive asit typically is designed to have very low failure rates and maintenancerequirements in order to reduce the need for technician trips up thetower to service the equipment. The inclusion of an additional DC-to-DCconverter 42 also represents a further increase in capital expenditures,which must be weighed against the anticipated savings in operatingcosts.

Thus, pursuant to embodiments of the present invention, a DC powersignal may be supplied to a tower-mounted remote radio head (or otherequipment) of a cellular base station over a power cable, where the DCpower signal that is supplied to the remote radio head may have, forexample, a relatively constant voltage level or a voltage level within apre-selected range, regardless of the current drawn by the remote radiohead. The voltage level of the DC power signal supplied to the remoteradio head may be set to be at or near a maximum power signal voltagethat the remote radio head can handle, thereby reducing the power lossof the DC power signal. In this manner, the operating costs for thecellular base station may be reduced.

In some embodiments, the programmable power supply according toembodiments of the present invention may comprise a DC-to-DC converterthat may be connected between a power supply of an existing base stationand the power cable that supplies the power signal to a tower-mountedremote radio head. Thus, by adding a single piece of equipment at thebottom of the tower, an existing cellular base station may beretrofitted to obtain the power savings available using the techniquesaccording to embodiments of the present invention.

While the above-described embodiments of cellular base stationsaccording to embodiments of the present invention include a first,conventional DC power supply 26 and a second DC-to-DC converter powersupply 28, it will be appreciated that in other embodiments these twopower supplies may be replaced with a single programmable power supplythat may be configured to output a relatively constant voltage at thefar end of the power cable 36 in the manner described above.

Pursuant to further embodiments of the present invention, a feedbackloop may be used to control the voltage of the DC power signal output bythe DC power supply so that the voltage of the DC power signal at thefar end of the power cable that connects the power supply and the remoteradio head is maintained at a desired level or within a desired range.FIG. 8 is a simplified, schematic view of one example embodiment of acellular base station 400 that implements such a technique.

As shown in FIG. 8 , the cellular base station 400 is similar to thecellular base station 100 described above with reference to FIG. 3 ,except that the cellular base station 400 further includes a DC powersignal voltage control module 50 that is co-located with the remoteradio head 24′. The DC power signal voltage control module 50 may belocated, for example, at or near the top of the tower 30. In an exampleembodiment, the DC power signal voltage control module 50 may include avoltage meter 52, a controller 54 and a communications module 56. Thevoltage meter 52 may be used to monitor the voltage of the DC powersignal at the far end of the power cable 36 (i.e., at the top of thetower 30). Any appropriate voltage meter may be used that is capable ofmeasuring the voltage of the DC power signal at the far end of cable 36(or at another location proximate the remote radio head 24′) or that maymeasure other parameters which may be used to determine the voltage ofthe DC power signal at the far end of cable 36.

The voltage meter 52 may supply the measured voltage (or otherparameter) to the controller 54. The controller 54 may then control thecommunications module 56 to transmit the measured or calculated voltageof the DC power signal at the far end of power cable 36 to, for example,the second power supply 28. The controller 54 may comprise anyappropriate processor, controller, ASIC, logic circuit or the like. Thecommunications module 56 may comprise a wired or wireless transmitter.In some embodiments, the communications module 56 may comprise awireless Bluetooth transmitter or a cellular transmitter. In otherembodiments, the communications module 56 may communicate with thesecond power supply 28 over a separate wired connection. In still otherembodiments, the communications module 56 may communicate with thesecond power supply 28 by modulating a signal onto the power cable 36.In each case, the communications module 56 may transmit the measured orcalculated voltage of the DC power signal at the far end of power cable36 (i.e., at the top of the tower 30) to the second power supply 28. Thesecond power supply 28 may adjust the voltage of the DC power signalthat it outputs in response to these communications in order togenerally maintain the voltage of the DC power signal at the far end ofpower cable 36 at a desired and/or pre-selected level or range. Thus, inthis embodiment, an active feedback loop may be used to maintain thevoltage of the DC power signal at the far end of power cable 36 at thepre-selected level.

The power signal voltage control module 50 may be a standalone unit ormay be integrated with other equipment such as, for example, the remoteradio head 24′.

While the embodiments that have been described above deliver a DC powersignal over the power cable 36, it will be appreciated that in otherembodiments, an AC power signal may be used instead. For example, if theremote radio heads 24′ are designed to be powered by an AC power signalas opposed to a DC power signal, then the power supply 28 may output anAC power signal as opposed to a DC power signal, but may otherwiseoperate in the same fashion. Likewise, in embodiments that include aDC-to-DC converter 42 at the top of the tower 30, an AC-to-DC convertermay be used instead or, if the remote radio head 24′ is designed to bepowered by an AC power signal, the DC-to-DC converter 42 may be replacedwith a Buck AC-to-AC converter. Thus, it will be appreciated that theembodiments illustrated in the figures are exemplary in nature and arenot intended to limit the scope of the present invention.

In the various embodiments described above, a single power cable 36 hasbeen provided that connects the power supply 28 to the remote radio head24′. It will be appreciated, however, that the cabling connection forthe power signal between the power supply 28 and the remote radio head24′ may include multiple elements such as two or more power cables 36that are connected by connectors in other embodiments.

A method of powering a radio that is mounted on a tower of a cellularbase station according to embodiments of the present invention will nowbe described with reference to the flow chart of FIG. 9 . As shown inFIG. 9 , operations may begin with a user inputting information to aprogrammable power supply which may be used by the programmable powersupply to set a voltage level of the power signal that is output by theprogrammable power supply (block 300). This information may comprise,for example, an electrical resistance of a cabling connection betweenthe power supply and the radio or information regarding thecharacteristics of the cabling connection that may be used to calculatethis resistance. While not shown in FIG. 9 , it will be appreciated thatin other embodiments the programmable power supply may have thecapability to measure and/or calculate the resistance of the cablingconnection, thereby avoiding the need for any user input. Theprogrammable power supply may use this information to output a DC powersignal that is provided to the remote radio head over the cablingconnection (block 310). The current of the DC power signal that isoutput may then be measured (block 320). The programmable power supplymay then automatically adjust a voltage level of the power signal outputby the power supply in response to changes in the measured outputcurrent so that the power signal that is input to the remote radio headwill have a substantially constant, preselected voltage (block 330). Asshown in FIG. 9 , blocks 320 and 330 are then performed continuously atappropriate intervals in order to maintain the voltage level of thepower signal that is input to the remote radio head at the preselectedvoltage level.

Embodiments of the present invention provide power supplies for poweringradio equipment such as a remote radio head that is located remote fromthe power supply used to power the radio (e.g., the power supply is atthe base of a cellular tower and the radio is at the top of the tower)without receiving any feedback from the radio or from other equipment atthe remote location. The voltage of the DC power signal supplied by thepower supply to the radio over a cabling connection may be controlled tobe at a pre-selected level or within a pre-selected range. Thepre-selected level or range may be set to reduce or minimize powerlosses that may be incurred in transmitting the DC power signal over thecabling connection. The voltage of the DC power signal output by thepower supply may be varied based on variations in the current drawn fromthe power supply so that the voltage of the DC power signal at the radioend of the cabling connection may have, for example, a substantiallyconstant value. This value may be selected to be near a maximum valuefor the voltage of the DC power signal that may be input to the remoteradio head.

While typically the voltage of the DC power signal output by the powersupply will be adjusted to maintain the voltage of the DC power signalat the radio end of the cabling connection at a set level, it will beappreciated that some variation is to be expected because of the time ittakes the DC power supply to adjust the voltage of the DC power signalin response to changes in the current drawn. It will also be appreciatedthat the voltage of the DC power signal need not be maintained at aconstant level at the radio end of the cabling connection but, mayinstead have different characteristics (e.g., set to be maintainedwithin a predetermined range, set to return to a pre-selected levelwithin a certain time period, etc.) in some embodiments.

In some current cellular systems, the voltage drop that occurs on the DCpower signal that is delivered from a power supply located at the bottomof a cellular tower to the remote radio head at the top of the tower maybe so large that the voltage of the DC power signal at the top of thetower may be insufficient to run the remote radio head. As a result,larger diameter power cables are used in some cases that exhibit less DCresistance and hence a smaller voltage drop. However, the use of largerpower cables has a number of disadvantages, as these cables can besignificantly more expensive, add more weight to the tower (requiringthat the towers be constructed to handle this additional weight) andmore difficult to install.

Pursuant to embodiments of the present invention, this problem may bereduced or solved by controlling the voltage of the DC power signaloutput by the power supply so that the voltage of the DC power signal atthe radio end of the power cabling connection may be at or near amaximum voltage for the DC power signal that may be input to the remoteradio head. This scheme reduces the voltage drop of the DC power signal,and hence may allow for the use of smaller diameter power cables and/orlonger cabling connections between the power supply and the remote radiohead. Additionally, as noted above, as the power losses experienced bythe DC power signal are less, the costs of operating the remote radiohead may also be reduced.

As discussed above with reference to FIG. 4 , in some embodiments of thepresent invention, the resistance of the power cabling connectionbetween the power supply 28 at the bottom of the tower 30 and the remoteradio head 24′ at the top of the tower 30 may be measured or otherwisedetermined. This measured resistance is then used to set the voltage ofthe power supply signal output by the second power supply 28 in order tomaintain the voltage of the power supply signal that is supplied to theremote radio head 24′ at the top of the tower 30 at a relativelyconstant value despite variation in the current drawn by the remoteradio head 24′.

In some embodiments, the resistance of the power cabling connection maybe determined by sending two signals over the power cabling connectionthat have different voltages, and then measuring the current of thesesignals. So long as the power drawn by the remote radio head remainsconstant during the time that the two signals are transmitted, then theresistance of the power cabling connection may be calculated using knownrelationships between voltage, current, resistance and power.

In particular, based on Equations (1) and (2) above, the voltage of afirst power signal output from the power supply (V_(PS1)) relates to thecurrent flowing through the power cabling connection (I₁) and theresistance R_(Cable) of the power cabling connection as follows:V _(PS1) =V _(RRH1) +V _(Drop1) =V _(RRH1) +I ₁ *R _(Cable)  (5)where V_(RRH1) is the voltage of the first power signal as received atthe remote radio head, and where V_(Drop1) is the voltage dropexperienced by the first power signal in traversing the power cablingconnection to the remote radio head.

As noted above, it is assumed that the power (P) that is drawn by theremote radio head remains constant. The relationship between the voltageof the first power signal at the remote radio head and the power (P)drawn by the remote radio head is as follows:V _(RRH1) =P/I ₁  (6)

Combining Equations (5) and (6), the voltage of the first power signaloutput from the power supply (V_(PS1)) is as follows:V _(PS1) =P/I ₁ +I ₁ *R _(Cable)  (7)

Solving Equation (7) for the power (P):V _(PS1) −I ₁ *R _(Cable) =P/I ₁  (8)P=(V _(PS1) *I ₁)−(R _(Cable) *I ₁ ²)  (9)

In Equation (9), V_(PS1) is known (as the voltage of the first powersignal may be set to a predetermined value), and the value of I₁ ismeasured using, for example, a current sensor in the power supply. Thevalues of P and R_(Cable), however, may not be known.

As noted above, a second power signal (V_(PS2)) may then be output fromthe power supply and the current (I₂) of this second power signal ismeasured. Combining Equations (5) and (6) above with respect to thesecond power signal, the voltage thereof may be determined as follows:V _(PS2) =P/I ₂ +I ₂ *R _(Cable)  (10)

As noted above, if the power (P) drawn by the remote radio head remainsconstant, then P is the same in Equations (9) and (10). Accordinglyincorporating Equation (9) into Equation (10) for the power (P):V _(PS2)=[(V _(PS1) *I ₁)−(R _(Cable) *I ₁ ²)]/I ₂ +I ₂ *R_(Cable)  (11)

Solving Equation (11) for R_(Cable):V _(PS2) *I ₂ =V _(PS1) *I ₁ −R _(Cable) *I ₁ ² +I ₂ ² *R _(Cable)  (12)V _(PS2) *I ₂ −V _(PS1) *I ₁ =R _(Cable)(I ₁ ² +I ₂ ²)  (13)R _(Cable)=(V _(PS2) *I ₂ −V _(PS1) *I ₁)/(I ₁ ² +I ₂ ²)  (14)

Thus, so long as the power (P) drawn by the remote radio head remainsconstant, by sending two power signals having different voltages (namelyV_(PS1) and V_(PS2)) from the power supply and measuring the current ofthese signals (namely (I₁ and I₂), Equation (14) may be used todetermine the resistance R_(Cable) of the power cabling connection.

In order to reduce the likelihood that the power (P) drawn by the remoteradio head changes between the times that the first power signal and thesecond power signal are injected onto the power cabling connection, thefirst and second power signals may be transmitted with little delaytherebetween. As the currents I₁ and I₂ can be measured very quickly, itmay be possible to send the first and second power signals and measurethe currents thereof within a very short timeframe such as, for example,a millisecond or even less. Moreover, in some embodiments, the systemmay be programmed to transmit more than two power signals havingdifferent voltages to the remote radio head and measuring the associatedcurrents of these signals in order to either (1) identify and discardpower signals that were transmitted during a time when the power (P)drawn by the remote radio head changed or (2) reduce the impact of anysuch measurements that are made when the power drawn by the remote radiohead changed by averaging those measurements with a large number ofmeasurements that were taken at times when the power drawn by the remoteradio head did not change.

In some embodiments, the resistance R_(Cable) of the power cablingconnection may be calculated using a running average of the voltages andmeasured currents of a series of power signals that are transmitted overthe power cabling connection. For example, if a total of X power signalshaving different voltages are transmitted over the power cablingconnection, the resistance R_(Cable) of the power cabling connection maybe determined as follows:R _(Cable)=Σ[(V _(PSn+1) *I _(n+1) −V _(PSn) *I _(n))/(I _(n+1) ² +I_(n) ²)]/X  (15)where the summation is performed from n=1 to (X−1).

The resistance R_(Cable) of the power cabling connection may change overtime based on a number of factors such as, for example, changes in theambient temperature, variation in the current drawn (which can affectthe temperature), corrosion on the power cable or connectors, andvarious other factors. These changes, however, tend to not be large andtend to occur gradually over time. By way of example, the resistance ofcopper changes at a rate of about 0.4% for each change in temperature byone degree Celsius. Thus, if over the course of a day the temperaturechanges from 80° F. (26.7° C.) to 50° F. (10° C.), the resistance of thepower cabling connection may change by nearly 7%. However, forresistance measurements obtained using the above-described techniquesthat are taken on the order of seconds (or less) apart, the change inresistance due to temperature changes will be almost zero.

In some embodiments, the resistance R_(Cable) of the power cablingconnection may be determined using Equation (15) above where “X” is setto a relatively large number (e.g., 100, 1000, etc.). Herein, theelements of the summation in Equation (15) for each different value of“n” may be referred to as a “sample.” Using as an example the case whereX is set to 500, the voltage of the power supply signal output by thepower supply may be varied 500 times and the resistance corresponding toeach different voltage may then be measured. By way of example, if atthe start of the resistance measurement procedure the power supply isoutputting a power supply signal having a voltage of 58 Volts so as toprovide a power signal at the input of the remote radio head having adesired voltage (e.g., between 54-56 Volts), during the resistancemeasurement the voltage of the power supply signal might be toggledevery 10 milliseconds between 58 Volts and 57.5 Volts. In this case, thesummation in Equation (15) would have 499 samples, and assuming that thecurrent drawn by the remote radio head does not change, each of thesesamples should theoretically have the same value, although, measurementerror, noise, changes in temperature and the like will in practiceintroduce a small amount of variation. After the 499 samples included inthe summation of Equation (15) in this example are determined, they maybe reviewed and any sample that appears as an outlier may be discarded,as the outliers are likely associated with a change in the power drawnby the remote radio head. The outliers may be particularly easy toidentify as they may tend to occur in consecutive locations in thesummation if the voltage of the power supply single is toggled at anappropriate rate.

In the above approach, any appropriate technique may be used foridentifying and discarding outliers among the samples summed in Equation(15). In one embodiment, samples that vary by more than a predeterminedamount from, for example, an average value may be discarded. In anotherembodiment, samples that vary by more than a predetermined percentagefrom an average or median value of a large group of samples that allhave approximately the same value may be discarded. Many otheralgorithms or techniques may be used. In this fashion, distortions thatmight otherwise be introduced in the resistance calculation can beavoided or at least reduced.

By way of example, after computing the 499 samples in theabove-described embodiment, a median value of the 499 samples may bedetermined. Ones of the 499 samples that deviated from the median sampleby more than a pre-determined amount such as, for example, apre-selected percentage (e.g., 5%), might then be discarded. Theremaining samples may then be summed to determine the resistance of thepower cabling connection.

In other embodiments, the resistance R_(Cable) of the power cablingconnection may be determined using Equation (15), even though some errormay be introduced by samples taken during periods when the power drawnby the load changed. This approach will introduce some amount of error,although the degree of error may be reduced by performing the resistancecalculation more often and/or by using larger numbers of samples.

One advantage of the above-described approaches for determining theresistance R_(Cable) of the power cabling connection is that it allowscalculation of the resistance during normal operation by simply togglingor otherwise adjusting the voltage of the power supply signal a smallamount during normal operation. The amount of the voltage swing may beselected based on a variety of different factors. Moreover, while in theabove examples the voltage is toggled between two different values, itwill be appreciated that more than two values may be used.

It should also be noted that an initialization procedure may be usedwhen the cellular base station first goes operational, as initially theappropriate voltage level for the power supply signal may not be known.In this case, a relatively low power supply voltage may be used that isless than the maximum operating voltage of the remote radio head toensure that a power supply signal having too large a voltage level isnot supplied to the remote radio head. Once a resistance measurement hasbeen performed, the voltage levels of the power supply signal may beincreased by an appropriate amount in view of the measured resistanceand the loading of the remote radio head.

One or more of the techniques for determining the resistance of thepower cabling connection that are described above may then be performedon a periodic or non-periodic basis. In this manner, changes in theresistance of the power cabling connection may be identified and thevoltage of the power supply signal may be adjusted accordingly. Betweena hot summer day and a cold winter night the temperature might vary byas much as 100° F. (55° C.), which corresponds to more than a 20% changein the resistance of the power cabling connection. By adjusting thepower supply voltage to account for such changes in the resistance, thecurrent of the power supply signal may be reduced by a correspondingamount, which may result in significant power savings since the powerloss due to the voltage drop varies according to the square of thecurrent.

In some embodiments, the power supply 150 of FIG. 5 may be used tomeasure the resistance based on the above-described techniques. Thecontrol logic 162 may toggle the voltage of the power signal output bythe power supply 150 in the manner described above, and the currentsensor 158 may sense the current of the power signal associated witheach different voltage value. The control logic 162 may identify anddiscard outlying samples using, for example, one of the techniquesdiscussed above, and may determine the resistance of the power cablingconnection according to Equation (15).

One potential problem with setting the voltage of the power supplysignal that is output by the power supply to a voltage that will resultin the power supply signal having a voltage at the remote radio headthat is near the maximum specified voltage that the remote radio headmay handle is the possibility that power supply signal that is input tothe remote radio head may occasionally have a voltage that exceeds themaximum specified power supply voltage for the remote radio head. Thismay occur, for example, if there is a sudden decrease in the amount oftraffic supported by the remote radio head, which will in turn result ina sudden decrease in the current drawn by the remote radio head. Thissudden drop in current may significantly reduce the voltage drop alongthe power cabling connection, thereby increasing the voltage of thepower signal received at the remote radio head. While the power suppliesaccording to embodiments of the present invention are designed to adjustthe voltage of the power supply signal to compensate for this drop incurrent, if the voltage of the power supply signal is not adjustedquickly enough, the reduction in the voltage drop may result in thepower supply signal at the remote radio head having a voltage thatexceeds the maximum specified power signal voltage for the remote radiohead. As this may damage the remote radio head, suitable margins may bebuilt into the system to protect the remote radio heads from suchpossible damage.

Moreover, rapid changes in the current flowing through the power cablemay also result in a temporary change in the voltage of the power signaldue to the inductance of the cable. When the current of the power signalis rapidly increased, this may result in a phenomena known as the dI/dtvoltage drop, which may be determined as follows:V _(dI/dt Drop) =L*(dI/dt)  (16)where L is the cumulative inductance of the conductors and dI/dt is therate of increase in the current flowing through the conductors withrespect to time. When the current of the power signal is rapidlydecreased, the reverse process happens, which may result in a temporaryincrease in the voltage of the power signal, which is referred to hereinas a “dI/dt voltage spike.”

Pursuant to further embodiments of the present invention, a shuntcapacitance unit may be provided between the two conductors of a powercable that is used to provide a DC power signal to a remote radio head.This shunt capacitance unit may be implemented, for example, using oneor more capacitors that are coupled between the power supply and returnconductors of the power cable. The shunt capacitance unit may dampenincreases in the voltage of the power signal that result from changes inthe current drawn by the remote radio head and by the above-discusseddI/dt voltage spikes. As such, a sudden decrease in the current level ofthe power signal due to a sudden drop in the loading of the remote radiohead may result in a smaller and slower reduction in the voltage drop,and hence the shunt capacitance unit may help protect the remote radiohead from situations where the current of the power signal drops morequickly than the voltage of the power signal output by the power supplycan be adjusted.

By way of example, a remote radio head that is located atop a largeantenna tower may specify a maximum voltage of 58 Volts for the powersignal. Pursuant to embodiments of the present invention, the voltage ofthe power signal at the output of the power supply (which is located atthe bottom of the tower) that is used to power this remote radio headmay be adjusted so that the power signal at the input to the remoteradio head has a voltage of approximately 55 Volts. In situations wherethe remote radio head is drawing a large amount of current, the powersupply may output a power signal having a voltage of, for example, 62volts in order to supply a power signal having 55 Volts to the remoteradio head due to the large I²R power loss along the power cablingconnection between the power supply and the remote radio head. If all ofthe traffic to the remote radio head suddenly drops, the current drawnby the remote radio head will decrease in a dramatic fashion, as willthe I²R power loss along the power cabling connection. As a result, thevoltage of the power signal that is delivered to the remote radio headmay be on the order of 60 Volts or more if the power supply fails toadjust the output voltage quickly enough, and this 60 Volt power signalmay potentially damage electronics in the remote radio head.

FIG. 10 is a schematic diagram that illustrates a trunk cable assembly500 that may used, for example, to implement the trunk cable 40 of acellular base station. The trunk cable assembly 500 includes nineindividual power cables and nine sets of four optical fibers, and henceis suitable for transmitting power and data to a cellular base stationthat includes nine remote radio heads. As an example, if the cellularbase station 100 of FIG. 3 were modified to include nine baseband units22, remote radio heads 24 and twenty-seven antennas 32, then the trunkcable 500 of FIG. 10 would be a suitable replacement for the trunk cable40 illustrated in FIG. 3 . The trunk cable 500 includes shuntcapacitances between the two conductors of each of the nine power cablesthat are used to provide DC power signals to the nine remote radio heads24. These shunt capacitances may dampen increases in the voltage of theDC power signals that may result from changes in the current drawn bythe remote radio head and by associated dI/dt voltage spikes in order toprotect the remote radio heads from overshooting the maximum specifiedvoltage for the power signal input thereto.

As shown in FIG. 10 , the trunk cable assembly 500 comprises a hybridpower/fiber optic cable 510, a first breakout canister 530 and a secondbreakout canister 550. The hybrid power/fiber optic cable 510 has nineindividual power cables 512 (the callout in FIG. 10 depicts three ofthese individual power cables 512) that may be grouped together into acomposite power cable 518 and a fiber optic cable 520 that includesthirty-six optical fibers 522. The fiber optic cable 520 may comprise ajacketed or unjacketed fiber optic cable of any appropriate conventionaldesign. The composite power cable 518 and the fiber optic cable 520 maybe enclosed in a jacket 524. While one example hybrid power/fiber opticcable 510 is shown in FIG. 10 , it will be appreciated that anyconventional hybrid power/fiber optic cable may be used, and that thecable may have more or fewer power cables and/or optical fibers. Anexemplary hybrid power/fiber optic cable is the HTC-24SM-1206-618-APVcable, available from CommScope, Inc. (Hickory, N.C.).

The first breakout canister 530 comprises a body 532 and a cover 536.The body 532 includes a hollow stem 534 at one end that receives thehybrid power/fiber optic cable 510, and a cylindrical receptacle at theopposite end. The cover 536 is mounted on the cylindrical receptacle toform the breakout canister 530 having an open interior. The hybridpower/fiber optic cable 510 enters the body 532 through the stem 534.The composite power cable 518 is broken out into the nine individualpower cables 512 within the first breakout canister 530. Each individualpower cable 512 includes a power supply conductor 514 and a returnconductor 516. The nine individual power cables 512 are routed throughrespective sockets 538 in the cover 536, where they are received withinrespective protective conduits 540 such as a nylon conduit that may besufficiently hardy to resist damage from birds. Thus, each individualpower cable 512 extends from the first breakout canister 530 within arespective protective conduit 540. The optical fibers 522 are maintainedas a single group and are routed through a specific socket 538 on thecover 536, where they are inserted as a group into a conduit 542. Thus,the first breakout canister 530 is used to singulated the nine powercables 512 of composite power cable 518 into individual power cables 512that may be run to respective remote radio heads 24, while passing allof the optical fibers 522 to a separate breakout canister 550.

As shown in the inset of FIG. 10 , a plurality of shunt capacitanceunits in the form of ceramic capacitors 548 are provided within thefirst breakout canister 530. Each capacitor 548 is connected between thepower supply conductor 514 and the return conductor 516 of a respectiveone of the individual power cables 512. For low frequency signals suchas a DC power signal, the shunt capacitors 548 appear as an opencircuit, and thus the DC power signal that is carried on each individualpower cable 512 will pass by the respective shunt capacitors 548 to theremote radio heads 24. However, as discussed above, during periods wherethe current carried by an individual power cable 512 drops in responseto a decreased loading at the remote radio head 24, the shunt capacitor548 may act to reduce the magnitude of the dI/dt voltage spike on the DCpower signal.

As noted above, the optical fibers 522 pass through the first breakoutcanister 530 as a single unit in conduit 542 which connects to thesecond breakout canister 550. In the second breakout canister 550, thethirty-six optical fibers 522 are separated into nine optical fibersubgroups 552. The optical fiber subgroups 552 are each protected withina respective conduit 554. The second breakout canister 550 may besimilar to the first breakout canister 530 except that it is used tobreak out the thirty-six optical fibers 522 into nine sets of fouroptical fibers that are fed into nine respective protective conduits552.

As discussed above, rapid changes in the power drawn by a remote radiohead 24 may result in an increase in the voltage of the power signalreceived at the remote radio head 24 because (1) the power supply 28requires some amount of time to sense the reduction in current drawn bythe remote radio head 24 and to adjust the voltage of the power supplysignal in response thereto and (2) a sudden decrease in the currentdrawn by the remote radio head 24 may result in a dI/dt voltage spikethat momentarily increases the voltage of the power signal at the inputto the remote radio head 24. By providing power cables such as thehybrid power/fiber optic cable assembly 500 of FIG. 10 that have shuntcapacitors 548 integrated into each individual power cable 512, it ispossible to dampen such increases in the voltage of the power signalreceived at the remote radio head 24, thereby protecting the remoteradio head 24 from unintended spikes in the voltage of the power signalthat exceed the maximum voltage for the power signal that is specifiedfor the remote radio head.

Those of skill in this art will appreciate that the shunt capacitances548 may be provided in any number of forms. For example, a shuntcapacitance unit may be in the form of individual components, such asone or more capacitors, or in the form of other physical structures suchas parallel conductors separated by an air gap that may act like acapacitor. The amount of shunt capacitance provided may vary dependingon a number of factors including, for example, how close the voltage ofthe power signal that is input to the remote radio head 24 is to themaximum specified power signal voltage for the remote radio head 24.Generally speaking, the amount of shunt capacitance may be on the orderof hundreds, thousands, tens of thousands, or hundreds of thousands ofmicrofarads in some embodiments.

The use of shunt capacitance units is disclosed in U.S. PatentApplication Publication No. 2015/0080055 (“the '055 publication”),although primarily for purposes of dampening a dI/dt voltage drop thatmay occur in response to sharp increases in the current drawn by aremote radio head. As discussed above, it has been discovered that theuse of such a shunt capacitance unit may also be used to protect theremote radio head from situations in which the voltage of the powersignal would exceed the maximum power supply voltage specified for theremote radio head by slowing the decrease in the voltage drop andthereby providing the power supply additional time to adjust to thereduced loading at the remote radio head. The '055 publication disclosesa variety of ways in which the shunt capacitance unit may beimplemented, all of which may be used according to embodiments of thepresent invention to protect a remote radio head from situations wherethe voltage of the power signal that is delivered to the remote radiohead could overshoot the maximum specified voltage for the remote radiohead. The entire content of the '055 publication is incorporated hereinby reference in its entirety.

It will also be appreciated that the shunt capacitance units may beplaced in a variety of locations other than within a trunk cable asshown in the embodiment of FIG. 10 . For example, in many cellular basestations, fiber optic and power jumper cables extend between a breakoutenclosure of a trunk cable (e.g., the breakout canisters 530, 550 ofFIG. 10) and the remote radio heads. In some cases, separate powerjumper cables and fiber optic jumper cables are provided, while in othercases composite jumper cables that include both optical fibers and powerconductors (which are separately connectorized) may be used to connecteach remote radio head to the junction enclosure. The jumper cables aremuch shorter in length than the trunk cables, as the breakout enclosureis typically located only a few feet from the remote radio heads,whereas the trunk cable is routed tens or hundreds of feet up theantenna tower. Additionally, the jumper cables include far fewercomponents. As such, trunk cables are typically far more expensive thanjumper cables.

In some embodiments, the shunt capacitance units may be implemented inthe power jumper cables or at other locations near the power inputs tothe respective remote radio heads. Implementing the shunt capacitanceunits in the jumper cables may provide a more efficient andcost-effective way of retrofitting existing cellular base stations toinclude shunt capacitance units. Additionally, jumper cables may beeasily replaced by a technician as they are designed to be connected anddisconnected, and jumper cable replacement does not raise environmentalsealing concerns as does opening a junction enclosure such as a breakoutcanister of a trunk cable.

FIG. 11 is a schematic drawing illustrating how a jumper cable 630having an associated shunt capacitance unit 650 according to embodimentsof the present invention may be used to connect a junction enclosuresuch as a breakout canister of a trunk cable to a remote radio head.FIG. 12 is a partially-exploded perspective view of an exampleembodiment of the shunt capacitance unit 650. As shown in FIGS. 11-12 ,a trunk cable 610 is terminated into or includes a junction enclosure620 at, for example, the top of an antenna tower (not shown). The jumpercable 630 connects the junction enclosure 620 to a remote radio head640. The jumper cable 630 includes a cable segment 631 that has a powersupply conductor 632 and a return conductor 633 that are electricallyinsulated from each other (see FIG. 12 ). In some embodiments, the powersupply conductor 632 and the return conductor 633 may each comprise aninsulated 8-gauge to 14-gauge copper or copper alloy wire.

A protective jacket 634 may enclose the power supply and returnconductors 632, 633. First and second connectors 635, 636 are terminatedonto either end of the cable segment 631. The first connector 635 isconfigured to connect to a mating connector 622 on the junctionenclosure 620, and the second connector 636 is configured to connect toa mating connector 642 of the remote radio head 640. The connectors 622,642 may be identical so that either of connectors 635 and 636 may beconnected to either of the connectors 622, 642. The jumper cable 630 mayinclude an associated shunt capacitance unit 650 that may be implementedin a variety of locations.

As shown in FIG. 12 , the shunt capacitance unit 650 may be implementedas a sealed unit that is interposed along the cable segment 631. Theshunt capacitance unit 650 may have a housing 660 that includes housingpieces 670, 680 that have respective cable apertures 672, 682 that allowthe cable segment 631 to pass through the housing 660. The shuntcapacitance 650 is implemented using a pair of electrolytic capacitors690, 692 that are connected in parallel between the power supplyconductor 632 and the return conductor 633. The capacitors 690, 692 mayhave a total capacitance of, for example, between 400 and 2500microfarads.

The capacitors 690, 692 may comprise non-polar electrolytic capacitorsand hence the jumper cable 630 may be installed in either directionbetween the junction enclosure 620 and the remote radio head 640. A fusecircuit 694 may be provided along the shunt path between the powersupply and return conductors 632, 633 that creates an open circuit inthe event of failure of the capacitors 690, 692.

While FIG. 12 depicts a jumper cable having a shunt capacitance unit 650implemented along the cable thereof, it will be appreciated that inother embodiments the shunt capacitance unit 650 may be implemented inone of the connectors 635, 636 of the jumper cable 630. In still otherembodiments, the shunt capacitance unit 650 may be implemented as astand-alone unit that may be connected, for example, between thejunction enclosure 620 and a conventional jumper cable or between theremote radio head 640 and a conventional jumper cable.

Pursuant to still further embodiments of the present invention, aprotection circuit in the form of an avalanche diode may be coupled inparallel with one of the above-described shunt capacitance units 548,650 that may be implemented along the power cables of a trunk cable, ofa jumper cable, or as a standalone unit. FIG. 13 is a circuit diagram ofa shunt capacitance unit 650′ that includes such an avalanche diode. Asshown in FIG. 13 , the shunt capacitance unit 650′ is identical to theshunt capacitance unit 650 of FIG. 12 , except that the shuntcapacitance unit 650′ further includes an avalanche diode 696 that ispositioned between the power supply conductor 632 and the returnconductor 633 of the jumper cable, in parallel to the capacitors 690,692. The diode 696 is designed to be non-conducting under normaloperating conditions, but to start conducting at higher reverse biasvoltages. For instance, in one example embodiments the diode 696 may bedesigned to be non-conducting at reverse bias voltages that are atsomewhere between 0.5 Volts and 3 Volts less than the maximum specifiedvoltage for the power supply signal that is provided to the remote radiohead, but to start conducting at higher reverse bias voltages. It willbe appreciated, however, that the avalanche diode 696 may be designed tooperate at other voltage margins in other embodiments. The reversebreakdown voltage of the avalanche diode 696 may be selected based on amaximum specified voltage for the power supply signal that is providedto the remote radio head. Thus, if the voltage of the DC power signal atthe input to the remote radio head starts to approach the maximumspecified power signal voltage for the remote radio head, the avalanchediode 696 experiences reverse breakdown and will provide a bypasscurrent path.

In the embodiment of FIG. 13 , the diode 696 may be more effective thanthe capacitors 690, 692 in absorbing voltage spikes to ensure that thevoltage of the power supply signal does not exceed the maximum specifiedpower signal voltage for the remote radio head. If the voltage of thepower signal spikes above the reverse breakdown voltage of the avalanchediode 696, the voltage across the diode 696 will be held substantiallyat the reverse breakdown voltage for the duration of the voltage spike(i.e., until the programmable power supply regulates the voltage). Insome embodiments of FIG. 13 , the shunt capacitors 690, 692 and/or thefuse circuit 694 may be omitted so that the circuit 650′ will simply bea protection circuit without any shunt capacitance.

A diode such as, for example, the avalanche diode 696 that is includedin the embodiment of FIG. 13 , may also be used to measure theresistance of the power cabling connection according to furtherembodiments of the present invention. In particular, a reverse DCvoltage may be applied across the power supply and return conductors632, 633, and the reverse current in response to this reverse voltagemay be measured using, for example, the resistance measurement circuit170 of the programmable power supply (see FIG. 5 ). The reverse voltageacross the input to the remote radio head will be limited to the forwardvoltage across the avalanche diode 696, which will be less than 1 Volt,and hence will not be harmful to the remote radio head. While thismeasurement cannot be done during normal operation of the remote radiohead (as the reverse DC voltage is applied as opposed to the normalpower supply signal), this technique may be performed, for example, aspart of the qualification of a new cellular base station to measure theresistance of the power cabling connection thereof. It will beappreciated that other types of diodes such as a p-n diode or a Schottkydiode may be used in place of the avalanche diode 696 for purposes ofmaking such a resistance measurement. The use of the avalanche diode 696additionally provides the above-described over-voltage protectionfeature.

Moreover, as shown in FIG. 14 , in a further embodiment, a diode 697 maybe added in series along the power supply conductor 632 in between theshunt paths for the avalanche diode 696 and the capacitor 690.Alternatively, diode 697 may be reversed and placed in the correspondinglocation along return conductor 633. The capacitor 690 may hold thevoltage to the remote radio head for the very short time periodnecessary to measure the reverse current when the reverse voltage isapplied as discussed above. The diode 697 may prevent the capacitor 690from discharging through resistance measuring circuit during periodswhen the reverse voltage is applied. Thus, the circuit 650″ of FIG. 14may be used to measure the resistance of the power cabling connectionduring normal operation of the remote radio head by quickly applying thereverse voltage and measuring the reverse current during normaloperation. In other embodiments the circuit of FIG. 14 may furtherinclude the fuse circuit 694 and/or the second capacitor 692 that areshown in FIG. 13 .

FIG. 15 is a schematic block diagram illustrating selected elements of acellular base 700 according to further embodiments of the presentinvention. The cellular base station 700 uses a so-called “power bus”power cable 710 that has a single power supply conductor 712 and asingle return conductor 714. These conductors 712, 714 are typicallymuch larger than the conductors provided in a power cable that includesa separate pair of power supply and return conductors for each remoteradio head. The pair of conductors 712, 714 are used to provide powersignals to a plurality of remote radio heads 724. The power bus cable710 includes a junction enclosure 716, and individual power jumpercables 730 may be used to connect each remote radio head 724 to thepower supply and return conductors 712, 714 of the power bus cable 710.The power bus cable 710 may be a standalone power cable or may be partof a trunk cable that also includes optical fibers that carry databetween the remote radio heads 724 and baseband units (not shown).

The use of power bus power cables such as cable 710 in the cellular basestations according to embodiments of the present invention may havecertain advantages. In particular, the current drawn over the power buscable 710 will be the current required by all of the remote radio heads724 that are powered over the power bus cable 710. As state-of-the-artcellular base stations now often have twelve (or more) remote radioheads 724, the current drawn over the pair of conductors 712, 714 willbe the total current drawn by all twelve remote radio heads 724. Thus,large changes in the current drawn by one of the remote radio heads thatwould normally require a large adjustment in the output voltage of thepower supply signal are smoothed out since any one remote radio head 724will only be drawing, on average, one twelfth of the current carriedover the power bus cable 710.

While embodiments of the present invention are primarily described abovewith respect to cellular base stations that have conventional antennatowers, it will be appreciated that the techniques and systems describedherein may be applied to a wide variety of other cellular systems. Forexample, cellular service is often provided in tunnels by locating thebaseband equipment and power supply in an enclosure and then connectingthis equipment to remote radio heads and antennas via long horizontaltrunk cables. Very long cabling connections may be used in someinstances, and the voltage drop along the cable may be particularlyproblematic in such installations. Similarly, in some metrocellarchitectures, the same concept is applied above-ground, with the remoteradio heads and antennas typically mounted on smaller, pre-existingstructures such as utility poles, buildings and the like. Once again,the trunk cables connecting the baseband equipment and power supplies tothe distributed remote radio heads and antennas may be very long (e.g.,a kilometre or more in some cases), and hence voltage drop likewise maybe a significant problem. Any of the above-described embodiments of thepresent invention may be used in these or similar applications.

The present invention has been described with reference to theaccompanying drawings, in which certain embodiments of the invention areshown. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiments that arepictured and described herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout the specification anddrawings. It will also be appreciated that the embodiments disclosedabove can be combined in any way and/or combination to provide manyadditional embodiments.

It will be understood that, although the terms first, second, etc. areused herein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

Unless otherwise defined, all technical and scientific terms that areused in this disclosure have the same meaning as commonly understood byone of ordinary skill in the art to which this invention belongs. Theterminology used in the above description is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the invention. As used in this disclosure, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will also beunderstood that when an element (e.g., a device, circuit, etc.) isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

In the description above, when multiple units of an element are includedin an embodiment, each individual unit may be referred to individuallyby the reference numeral for the element followed by a dash and thenumber for the individual unit (e.g., antenna 32-2), while multipleunits of the element may be referred to collectively by their basereference numeral (e.g., the antennas 32).

It will be further understood that the terms “comprises” “comprising,”“includes” and/or “including” when used herein, specify the presence ofstated features, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,operations, elements, components, and/or groups thereof.

In the drawings and specification, there have been disclosed typicalembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth inthe following claims.

That which is claimed is:
 1. An apparatus, comprising: a power supplycomprising an output configured to be coupled by power conductors to adirect current (DC) power input of a radio; wherein the power supply isconfigured to: provide, during a time period, a first DC voltage levelat the output of the power supply, wherein during the time period aconstant DC power level is drawn by the DC power input of the radiothrough the power conductors; when providing during the time period thefirst DC voltage level at the output of the power supply, then measure afirst direct current level flowing through the output of the powersupply; provide, during the time period, a second DC voltage level atthe output of the power supply; when providing during the time periodthe second DC voltage level at the output of the power supply, thenmeasure a second direct current level flowing through the output of thepower supply, wherein the second DC voltage level differs from the firstDC voltage level; and determine a resistance of the power conductorsusing the first DC voltage level, the second DC voltage level, the firstdirect current level, and the second direct current level.
 2. Theapparatus of claim 1, wherein determining the resistance of the powerconductors further comprises determining the resistance of the powerconductors by a following equation:R _(Power Conductors)=(V _(PS2) *I ₂ −V _(PS1) *I ₁)/(I ₁ ² +I ₂ ²),wherein R_(Power Conductors) is the resistance of the power conductors,V_(PS1) is the first DC voltage level provided at the output of thepower supply, I₁ is the first direct current level flowing through theoutput of the power supply when providing the first DC voltage level atthe output of the power supply, V_(PS2) is the second DC voltage levelprovided at the output of the power supply, I₂ is the second directcurrent level flowing through the output of the power supply whenproviding the second DC voltage level at the output of the power supply.3. The apparatus of claim 1, wherein the power supply is furtherconfigured to determine the resistance of the power conductors using atleast three sets, wherein each set comprises a DC voltage level providedat the output of the power supply and a direct current level flowingthrough the output of the power supply when providing the DC voltagelevel at the output of the power supply, wherein each DC voltage levelof each set is different.
 4. The apparatus of claim 3, wherein, usingthe at least three sets, the resistance of the power conductors isdetermined by a following equation:R _(Power Conductors)=Σ[(V _(PSn+1) *I _(n+1) −V _(PSn) *I _(n))/(I_(n+1) ² +I _(n) ²)]/X, wherein R_(Power Concluders) is the resistanceof the power conductors, V_(PSn) is a DC voltage level, of an nth set,at the output of the power supply, V_(PSn+1) is a DC voltage level, ofan n+1 set, at the output of the power supply, I_(n) is a direct currentlevel, of the nth set, flowing through the output of the power supplywhen providing the V_(PSn) at the output of the power supply, I_(n+1) isa direct current level, of the n+1 set, flowing through the output ofthe power supply when providing the V_(PSn+1) at the output of the powersupply, X is a total number of sets, and n is an index number used toindicate the DC voltage level or the direct current level of the nthset.
 5. The apparatus of claim 1, further comprising: measuring a directcurrent level flowing through the output of the power supply; andadjusting a DC voltage level at the output of the power supply based atleast in part on the resistance of the power conductors and the measureddirect current level flowing through the output of the power supply. 6.The apparatus of claim 5, wherein adjusting the DC voltage level at theoutput of the power supply comprises setting the DC voltage level at theoutput of the power supply according to a following equation:V _(PS) =V _(Radio)+(I*R _(Power Conductors)), wherein, V_(PS) is the DCvoltage level at the output of the power supply, V_(Radio) is a DCvoltage at a DC power input of the radio, I is the direct currentflowing through the output of the power supply, and R_(Power Conductors)is the resistance of the power conductors.
 7. The apparatus of claim 5,wherein a DC voltage level at a DC power input of the radio issubstantially constant notwithstanding a variation in a level of directcurrent flowing through the output of the power supply.
 8. The apparatusof claim 5, wherein a DC voltage level at a DC power input of the radiois above a nominal DC input voltage rating of the radio and is less thana maximum DC input voltage level of the radio.
 9. The apparatus of claim8, wherein a magnitude the nominal DC input voltage rating of the radiois 48V.
 10. The apparatus of claim 8, wherein the DC voltage level atthe DC power input of the radio is within four volts of the maximum DCinput voltage level of the radio.
 11. The apparatus of claim 3, furthercomprising: measuring a direct current level flowing through the outputof the power supply; and adjusting a DC voltage level at the output ofthe power supply based at least in part on the resistance of the powerconductors and the measured direct current level flowing through theoutput of the power supply.
 12. The apparatus of claim 11, whereinadjusting the DC voltage level at the output of the power supplycomprises setting the DC voltage level at the output of the power supplyaccording to a following equation:V _(PS) =V _(Radio)+(I*R _(Power Conductors)), wherein, V_(PS) is the DCvoltage level at the output of the power supply, V_(Radio) is a DCvoltage at a DC power input of the radio, I is the direct currentflowing through the output of the power supply, and R_(Power Conductors)is the resistance of the power conductors.
 13. The apparatus of claim11, wherein a DC voltage level at a DC power input of the radio issubstantially constant notwithstanding a variation in a level of directcurrent flowing through the output of the power supply.
 14. Theapparatus of claim 11, wherein a DC voltage level at a DC power input ofthe radio is above a recommended DC input voltage level of the radio andis less than a maximum DC input voltage level of the radio.
 15. Theapparatus of claim 14, wherein an absolute value of the recommended DCinput voltage level of the radio is 48V.
 16. The apparatus of claim 14,wherein the DC voltage level at the DC power input of the radio iswithin four volts of the maximum DC input voltage level of the radio.17. A method of determining a resistance of power conductorselectrically coupling an output of a power supply to a direct current(DC) power input of a radio, comprising: providing, during a timeperiod, a first DC voltage level at the output of the power supply,wherein during the time period a constant DC power level is drawn by theDC power input of the radio through the power conductors; when providingduring a time period the first DC voltage level at the output of thepower supply, measuring a first direct current level flowing through theoutput of the power supply; providing, during the time period, a secondDC voltage level at the output of the power supply; when providingduring the time period the first DC voltage level at the output of thepower supply, measuring a second direct current level flowing throughthe output of the power supply, wherein the second DC voltage leveldiffers from the first DC voltage level; and determining the resistance,of the power conductors coupling the output of the power supply to theDC power input of the radio, using the first DC voltage level, thesecond DC voltage level, the first direct current level, and the seconddirect current level.
 18. The method of claim 17, wherein determiningthe resistance of the power conductors further comprises determining theresistance of the power conductors by a following equation:R _(Power Conductors)=(V _(PS2) *I ₂ −V _(PS1) *I ₁)/(I ₁ ² +I ₂ ²),wherein R_(Power Conductors) is the resistance of the power conductors,V_(PS1) is the first DC voltage level at the output of the power supply,I₁ is the first direct current level flowing through the output of thepower supply when providing the first DC voltage level at the output ofthe power supply, V_(PS2) is the second DC voltage level at the outputof the power supply, I₂ is the second direct current level flowingthrough the output of the power supply when providing the second DCvoltage level at the output of the power supply.
 19. The method of claim17, further comprising determining the resistance of the powerconductors using three or more sets, wherein each set comprises a DCvoltage level at the output of the power supply and a direct currentlevel flowing through the output of the power supply when providing theDC voltage level at the output of the power supply, wherein each DCvoltage level of each set is different.
 20. The method of claim 19,wherein, using the three or more sets, the resistance is determined by afollowing equation:R _(Power Conductors)=Σ[(V _(PSn+1) *I _(n+1) −V _(PSn) *I _(n))/(I_(n+1) ² +I _(n) ²)]/X; and wherein X is a total number of sets; whereinR_(Power Conductors) is the resistance of the power conductors, V_(PSn)is a DC voltage level, of an nth set, at the output of the power supply,V_(PSn+1) is a DC voltage level, of an n+1 set, at the output of thepower supply, I_(n) is a direct current level, of the nth set, flowingthrough the output of the power supply when providing the V_(PSn) at theoutput of the power supply, I_(n+1) is a direct current level, of then+1 set, flowing through the output of the power supply when providingthe V_(PSn+1) at the output of the power supply, and n is an indexnumber used to indicate the DC voltage or the direct current of the nthset.
 21. The method of claim 17, further comprising: measuring a directcurrent level flowing through the output of the power supply; andadjusting a DC voltage level at the output of the power supply based atleast in part on the resistance of the power conductors and the measureddirect current level flowing through the output of the power supply. 22.The method of claim 21, wherein a DC voltage level at the DC power inputof the radio is substantially constant notwithstanding a variation in alevel of direct current flowing through the output of the power supply.23. The method of claim 21, wherein a DC voltage level at the DC powerinput of the radio is above a nominal DC input voltage level of theradio and is less than a maximum DC input voltage level of the radio.24. The method of claim 23, wherein the DC voltage level at the DC powerinput of the radio is within four volts of the maximum DC input voltagelevel of the radio.
 25. The method of claim 19, further comprising:measuring a direct current level flowing through the output of the powersupply; and adjusting a DC voltage level at the output of the powersupply based at least in part on the resistance of the power conductorsand the measured direct current level flowing through the output of thepower supply.
 26. The method of claim 25, wherein a DC voltage level atthe DC power input of the radio is substantially constantnotwithstanding a variation in a level of direct current flowing throughthe output of the power supply.
 27. The method of claim 25, wherein a DCvoltage level at the DC power input of the radio is above a nominal DCinput voltage level of the radio and is less than a maximum DC inputvoltage level of the radio.
 28. The method of claim 27, wherein the DCvoltage level at the DC power input of the radio is within four volts ofthe maximum DC input voltage level of the radio.